An interconnected silicon–carbon conductive framework for dissipating mechanical strain for advanced Li-ion storage

Abstract

The ultra-high capacity of silicon (Si) holds great promise for high-energy density Li-ion batteries. Unfortunately, effective dissipation of the mechanical stress of Si while improving conductivity remains a great challenge. Here, Si@SiO_x nanoparticles (NPs) and polyvinyl alcohol were uniformly and effectively combined by the molecular self-assembly strategy. Using (NH₄)₂S₂O₃ as a foaming agent, freeze drying and in situ carbonization were employed to encapsulate the Si@SiO_x NPs into a porous interconnected three-dimensional carbon framework (FNS-Si@C). This structure simultaneously provides ideal mechanical strength, expansion buffer space and fast conductive connection to ensure the stability of the electrode and excellent reaction kinetics. The FNS-Si@C anode with high Si content (74 wt%) exhibited gratifying Li-ion reaction kinetics (1217 mA h g⁻¹ at 1000 mA g⁻¹), impressive cycling stability (678 mA h g⁻¹ after 650 cycles with 99.6% coulombic efficiency at 1000 mA g⁻¹) and favorable structural integrity (44.6% electrode expansion). Furthermore, the assembled full cell coupled with an LiFePO₄ cathode delivered outstanding Li-ion storage properties. This strategy of introducing Si into a solid skeleton with good conductivity and mechanical properties can also enhance the electrochemical performance of other alloy-type materials.